Photosensitive compositions are used in various fields including printing plates, color proofs, color filters, solder resists and photo-curing ink. In particular, in recent years, curing at room temperature, fast-curing and solvent absence, which are the most characteristic properties of photo-curing, have received attention in various fields including those applications from the viewpoints of environmental concerns, energy saving, safety in working, production costs and the like and many studies and developments have been made on photosensitive compositions.
Photosensitive compositions are each mainly composed of a photopolymerization initiator, a binder resin, a compound having an ethylenically unsaturated bond which cures by a polymerization reaction, and various kinds of additives, and the kinds of the components depend on use to which the photosensitive composition is applied.
The compounds which constitute the photopolymerization initiator are selected by their photosensitive wavelengths and polymerization initiating properties. The binder resin, the compound having an ethylenically unsaturated bond, and the additives are selected by polymerizability and physical properties of a desired cured product. They are used for a photosensitive composition in combinations.
However, some binder resins, some compounds each having an ethylenically unsaturated bond, and some additives occasionally cause problems as follows in the photosensitive compositions. (1) Sufficient energy for initiating photopolymerization is not obtained; (2) preservation stability is not obtained; (3) since irradiation light does not reach deep enough in a desired cured product owing to the thickness thereof, curing does not proceed sufficiently; (4) oxygen inhibition occurs at the portion where the photosensitive composition contacts the air; and (5) property of retaining a line width of fine line patterns at alkaline development is inferior.
For those problems, various measures have been taken; for example, irradiation with greater light energy, use of an excess amount of a photopolymerization initiator, and placement of an oxygen shielding membrane. Also for energy saving and reduction in production cost, a photosensitive composition having more excellent photosensitivity is desired.
Of those, in the development of color filters to be used for color televisions, liquid crystal display devices, solid-state image sensing devices, cameras and the like, pigment-dispersing resists for color filters have been studied for an improvement in productivity and high definition. In such applications, there have been growing demands on photosensitive compositions such as one to be cured at lower energy, one to be cured more quickly, one capable of forming finer patterns, and one having a greater depth of curing.
A color filter is usually manufactured by forming a lattice-like black-colored matrix (black matrix) on the surface of a transparent substrate such as glass or a plastic sheet and then forming three or more different hue patterns of red, green, blue and the like to an accuracy of several micrometers. Of those, the black matrix is arranged for improving contrast and preventing malfunction of TFT. Though a resist for forming the black matrix (black matrix resist) has a high light-blocking effect and thus can be hardly photo-cured by nature, high sensitivity has become demanded with growth in the size of a glass substrate to be used. At the same time, the black matrix resist with which no substantial change in line width of fine line patterns occurs even after being exposed to an alkaline developer for a long time, i.e., one having an excellent development latitude has been demanded strongly.
In late years, liquid crystal displays have come into use for television sets and thus demands have risen for color filters having excellent chromatic contrasts. In addition, there is a demand for a pigment in a concentrated amount but it may lead to less sensitivity. Therefore, for improving the sensitivity of the photosensitive composition and a black matrix resist composition for a color filter, the use of polyfunctional thiol compounds has been proposed (JP 10-253815 A, JP 10-253816 A, JP 10-253817 A, JP 2004-149755, etc.).
However, polyfunctional thiol compounds, which have been proposed heretofore, have aliphatic polyol components provided as their basic skeletons, so that photo-cured products thereof might cause a problem of smaller line widths of fine line patterns due to their inferior alkali-resistant development properties, although the sensitivity of the composition can be enhanced. In other words, there has been a problem of insufficient development latitude. In particular, for the black matrix resist on which lattice-like patterns should be formed, a phenomenon in which the line width of fine line patterns becomes small has become a very critical problem.